Our notion of secrecy between agents is analogous to causal independence between events in graphs used to study causality in physics.
Causal structures [1]}, [2]}, [3]}, [4]}, [5]}, [6]} try to capture the causal relations between events
within a larger context (Figure REF ). Both causality (as expressed by Reichenbach's principle) and secrecy are guiding principles of
a certain way of representing a theory (causal structures and restricted agents respectively) that help us understand a complex situation — they are
not necessarily fundamental features of the laws of nature. How useful the representation is depends both on the guiding principle and on the choice of
variables of interest (like events or agents).
